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大数据与网络安全论文范文英文版

发布时间:2024-09-06 09:56:35

大数据与网络安全论文范文英文版

Data Management1 why Data Management ? We have already considered hardware and software in some In this chapter, we turn our attention to a third basic computer resource, Many computer applications require that data be stored for subsequent [1] Simply storing the data is not enough, A typical computer system, even a small one, can have dozens of disks and tapes, each holding data for dozens of different For any given application, one and only one set of data will We must be able to store, Locate, and retrieve the specific data needed by a given That is the concern of data 2 Accessing DataImagine a single diskette containing several For a particular application, only one of those programs will How is a given program selected, loaded, and executed? In Chapter 6, we learned that the operating system, responding to a use’s command, reds the disk’s index, searches it for the requested program name, extracts the program’s track and sector address, and issues primitive commands to read it into main Later, following a RUN command, the program is given control of the Accessing data presents a similar A single diskette can hold data for several different For a given application, one and only one set of data will do, and finding the right data is much like finding the right There are differences between accessing programs and accessing data, When a program is need, all its instructions must be loaded into Data, on the other hand, are typically processed selectively, a few elements at Thus, it is not enough merely to locate the data; we must be able to distinguish the individual data elements, 1 Data Structures The key to retrieving data is remembering where they are stored, If the data elements are stored according to a consistent and well understood structure, it is possible to retrieve by remembering that The simplest data structure is a For example, data for a program that computes an average might be stored as a series of numbers separated by commas (F1) The commas distinguish the individual data Most programming languages support amore complex data structure called an array (Fig 2) Each array element can hold one data Each element is assigned a unique identifying number or numbers, and individual data elements can be inserted, extracted, or manipulated by referencing those For example, in the array pictured in F 2 elements are identified by a row number and a column number, and row 1, column3 (element1,3) contains the value Once an array has been filled, it can be written to disk, tape, or any other secondary medium, and back into memory for Consider a program that generates name and address For each label, we need a name, a street address, a city, a state, and a zip If we needed only a few labels, we might store the data in a list, but separating the elements would soon become An option is to set up an array of names and addresses, with each row holding the data for a single The only problem is that the entire array must be in main memory before the individual elements can be accessed, and main memory space is Thus, even with an array, we could generate relatively few F 1 The simplest data structure is a Separators, such as these commas, serve to distinguish individual Often, a “sentinel” value, such as a negative number, marks the end of the 4410, 843, 184, 31, 905, 6357, 44, 7702, 228, 59, -1 F 2 Most programming languages support a more complex data structure called an array Individual cells are assigned a number or numbers, and data values are inserted manipulated, and extracted by referencing those A better solution is to organize the data as a file (F3) All computer data begin as patterns of bits, On a file, the bits are grouped to form Groups of characters, in turn, form meaningful data elements called A group of related fields is a record the file is a set of related For example, in a name and address file, an individual’s name is a Each record holds a complete set of data for data for a single individual ( a name, a street address, and so on) he file consists of all the Fig 3 Characters are grouped to form Fields are prouped to form A file is a group of related The data in a file are processed record by Normally, the file is stored on a secondary medium such as Programs are written to read a process its fields, generate the appropriate output, and then read and process another Because only one record is in main memory at a time, very little memory is Because many records can be stored on a single disk, a great deal of data can be processed in this limited 2 Locating Files Imagine a file stored on The first step in accessing its data is finding the The task is much like finding a program, but there are Following a command such as LOAD or RUN, programs are loaded by the application Data, on the other hand, are processed by application programs, in the context of a program’s Typically, just before the data are required, the program asks the operating system to open the Each file has a name; the open logic ( 4 ) reads the index, searches it by name, and finds the address of the first record in the F4 when a file is opened, the disk index is read into main memory and searched for the desired file’s If the file name is found, the file’s start address is extracted from the 3 Locating Records Once a file has located, the process of accessing its records can When a program needs input data, it reads a record; when it is ready to output results, it writes a Note that these instructions deal with selected records, not with the entire We open We read and write Let’s examine the data accessing process more A programmer views data logically, requesting the next record, or the name and address for a particular The data are stored on a secondary medium such as To access a record physically, the disk drive must be give a set of primitive commands: seeks, reads, and The programmer thinks in terms of logical I/O The external device stores and retrieves physical sectors; it “thinks” in terms of physical I/O There must be a mechanism for translating the programmer’s logical requests to the appropriate physical commands (Fig 5) On small computers, much of the logic is found in the operating system’s input/output control system; on larger machines, access methods are Increasingly, the programmer’s logical data request is translated to physical form by a database management 4 The Relative Record Concept How does software, be it operating system, access method, or database software, find specific records in a file? [2] The key to many storage and retrieval techniques is the relative record Imagine a string of 100 Numbers indicate a given record’s position relative to the first record in the The file’s first record ( relative record 0 ) is at “ start of file plus 0 ”;Its second record is at “ start of file plus 1”, and so Access Methods Imagine preparing meeting announcements for a You need a set of mailing labels, and each member’s name and address is recorded on an index Probably the easiest way to generate the labels is to copy the data from the first card, turn to the second card and copy it, and so on, processing the records sequentially, form the beginning of the file to the Magazine publishers face the same problem with each new issue, but need mailing labels for tens of thousands of Rather than using index cards, they store customer data on disk or magnetic tape, one record per The easiest way to ensure that all labels are generated is to process the records in the order in which they are stored, proceeding sequentially from the fist record in the file to the To simplify handing, the records might be presorted by zip code or a mailing zone, but the basic idea of processing the data in physical order still How dos this relate to the relative record number concept? A relative record number indicates a record’s position on the With sequential access, processing begins with relative record 0, then moves to relative record 1, 2, and son Accessing data sequentially involves little more than For example, imagine a program has just finished processing relative record What is the next record? Obviously, relative record We’ve already seen how a relative record number can be converted to read them, or write them, in physical Processing records in sequence is not always For example, when a subscriber moves, his or her address must be changed in the fire searching for that subscriber’s record sequentially is like looking for a telephone number by starting with the first page of the telephone book and reading line and That’s no how we use a telephone Instead, knowing the record are stored in alphabetical order ,we quickly narrow our search to a portion of a single page and then begin reading the entries, ignoring the bulk of the data the way we use a telephone book is good example of direct, or random, A disk drive reads or writes one record at a To randomly access a specific record, all the programmer must do is remember its address, and ask for it the problem is remembering all those disk addresses, One solution is maintaining an index of the Again, we’ll use the name and address fire as an We want to access individual customer record by As the file is created, records are written one at a time, in relative record number Additionally, as each record is written, the customer name and the associated relative record number are recorded in an array or After the last record has been written to disk and its position recorded on the index, the index is itself Once the index has been created, it can be used to find individual Assume, for example, that Susan Smith has changed her To record her now address on the file, a program read the file index, search the index for her name, find her relative record number, compute the disk address, and read her record, change her address, rewrite the record to the same place on Note that this specific record is accessed directly, and that no other records in the file are The basic idea of direct access is assigning each record an easy to remember, logical, and then converting that key to a relative record number, Given this relative location, a physical address can be computed, and record Using an index is one technique for converting keys to physical An option is passing a numeric key to an algorithm and computing a relative record Both techniques have the same objective; converting a programmer’s logical data requests to physical Earlier in the chapter we identified the gap separating logical and physical I/O An access method is a software module that bridges this gap, converting logical keys to physical addresses, and issuing the appropriate primitive There are many variations of sequential, indexed, and direct organizations, and each one has its own access Using a variety of data access techniques can be confusing, and this is one reason for the growing popularity of database management systems4 Database Management There are problems with traditional data Many result from viewing applications For example, consider Most organizations prepare their payrolls by computer because using a machine instead of a small army of clerks saves Thus, the firm develops a payroll program to process a payroll file, Inventory, accounts receivable, accounts payable, and general ledger analysis are similar applications, so the firm develops an inventory program, and inventory file, an accounts receivable program, an accounts receivable file, and so Each program is independent, and each processes it own independent data Why is this a problem? For on thing, different application often need the same data For example, schools generate both bills and student grade View the applications The billing program reads a file of billing data, and the grade report program reads an independent file of grade The outputs of both program are mailed to each student’s home; thus, student names and addresses must be redundantly recorded on both What happens when a student moves? Unless both file are up data, one will be Redundant data are difficult to A more subtle problem is data Each access method has its own rules for storing and retrieving data, and certain “tricks of the trade” can significantly improve the efficiency of a given Bacause the motivation for using the computer is saving The programmer is often tempted to save even more by taking advantage of these Thus, the program’s logic becomes dependent upon the physical structure of the When a program’s logic is tied to its physical data structure, changing that structure will almost certainly require changing the As a result, programs using traditional access method can difficult to The solution to both problems is often organizing the data as a single, integrated The task of controlling access to all the data can then be concentrated in a centralized database management How dose the use of a centralized database solve the data redundancy problem? All data are collected and stored in a single place; consequently, there is one and only one of any given data When the value of an element ( an address, for example) changes, the single database copy is corrected, Any program requiring access to this data element gets the same value, because there is only on How dose a database help to solve the data dependency problem? Since the responsibility for accessing the physical data rests with the database management system, the programmer can ignore the physical data As a result, programs tend to be much less dependent upon their data, and generally much easier to Expect the trend toward database management to There are problems with traditional data Because different applications often require the same data, certain data elements may be stored in several different places, and such redundant data are difficult to Another problem is data If a program’s logic is too closely linked to the physical structure of its data, that program can be difficult to The solution to both problems is often collecting all the organization’s data in a centralized With a database, there is only one copy of each data element, so the data redundancy problem is Because every program must access data through a database management system, programs are insulated from the physical data structure; thus, data dependency is

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楼主 你至今还保留关于网络安全的英文文献吗??如果有的话 麻烦可以发给我吗?我的QQ:403577706 谢谢了!!

大数据与网络安全论文范文

安全伴我行安全,牵系着每一个人的生活。每当我走在上学、放学的路上,看到“车水马龙”,“人山人海”的热闹景象,看到身边飞驰而过的车辆,心里就会产生恐惧感。眼前浮现的一幕幕车毁人亡的画面,让我感到害怕。每当想到这里,我就十分紧张,真害怕第二天遇到车祸的就是我。大家可能看到过这样一个报道:2005年11月14日,是个阳光明媚的日子。山西沁源县第二中学的几百名师生正在马路边跑操,突然间,一辆大货车象一个发疯的恶魔碾向跑操的队伍,随着一片片惊呼和惨叫,21个鲜花般的生命永远的离开了这美好的世界。许多家长听到噩耗传来,一路上呼唤着孩子的名字,奔向现场,可是,任凭大人们怎样撕心裂肺地呼喊,他们永远也不能回应。这血的教训,给多少家庭带来痛苦,把多少幸福的家庭拆散。我国是一个人口大国,人多车多,使道路显得更加拥挤。据统计,我国每年因车祸死亡人数超过10万人,其中,儿童死亡人数近2万人,居世界之首。平均每5分钟就有1人死于车祸,而不到半小时就有一个孩子葬身车轮,这是多么惊人的数字。在这触目惊心的数字背后,有多少个家庭失去欢乐,多少个亲人痛不欲生,多少个生命之花永远凋零。想到这些,我抑制不住内心的激动,为遇难者留下同情的泪水,对肇事者产生无比的愤慨!然而,这些事故的发生,绝大多数都是因为人们的交通安全意识淡薄,不遵守交通法规造成的。作为一名合格的中学生,我们理应积极行动起来,从我做起,从身边做起。因此,我倡议:①全体同学要认真遵守《中学生守则》、《中学生日常行为规范》和交通法规。②校内文明守纪,楼道内轻声轻步,绝不打闹,不做危险的游戏。③校外一定要注意交通安全,走路要走人行道,过马路要走斑马线,不要翻越护栏。十字路口一定要看清红绿灯。④马路上行走时要集中精力,不看书、不听音乐、不打闹。“红灯短暂,生命无限”、“不怕百步远,只怕一步险”。其实,前人发明红绿灯是有原因的,不要怕麻烦,有句话说的好“红灯无数次,生命只一次”,红灯会闪烁无数次的,而生命只有一次,用完了就没有下一次了,在红灯没有灭的时候,我们绝对不可以冒险过马路,哪怕两边没有车,也绝对不能穿过马路。因此,同学们千万不要在马路上打闹,这样太危险。还有的惨剧是行人翻越护栏造成的,大家要不怕麻烦绕过护栏。为了我们的生命之花永远绽放,为了让所有的家庭幸福美满,亲爱的同学们,让安全永远伴随你我他吧!

事实上,所谓“大数据时代”的说法并不新鲜,早在2010年,“大数据”的概念就已由美国数据科学家维克托·迈尔·舍恩伯格系统地提出。他在 大数据时代一书中说,以前,一旦完成了收集数据的目的之后,数据就会被认为已经没有用处了。比如,在飞机降落之后,票价数据就没有用了;一个网络检索命令完成之后,这项指令也已进入过去时。但如今,数据已经成为一种商业资本,可以创造新的经济利益。数据能够成为一种资本,与移动互联网有密切关系。随着智能手机、平板电脑等移动数码产品的“白菜化”,Wi-Fi信号覆盖的无孔不入,越来越多的人不再有“在线时间”和“不在线时间”之分,只要他们愿意,便可几乎24小时一刻不停地挂在线上;在线交易、在线支付、在线注册等网络服务的普及固然方便了用户,却也让人们更加依赖网络,依赖五花八门的网上平台。而随着科技的进步,以往需要几盒软盘或一张光盘保存的信息,如今只需一片指甲盖大小的芯片,即可全部储存而且绰绰有余;以往需要电脑、显示器、读卡器等专门设备才能读取的数码信息载体,如今或许只需一部智能手机和一个免费下载的APP第三方应用程序,便可将数据一览无余。大数据时代的科技进步,让人们身上更多看似平常的东西成为“移动数据库”,如带有存储芯片的第二代银行卡、信用卡,带有芯片读取功能的新型护照、驾驶证、社保卡、图书证,等等。在一些发达国家,官方为了信息录入方便,还不断将多种“移动数据库”的功能组合成一体。数字化时代使得信息搜集、归纳和分析变得越来越方便,传统的随机抽样被“所有数据的汇拢”所取代,基于随机抽样而变得重要的一些属性,如抽样的精确性、逻辑思辨和推理判断能力,就变得不那么重要,尽可能汇集所有数据,并根据这些数据得出趋势和结论才至为关键。简单说,以往的思维决断模式是基于“为什么”,而在“大数据时代”,则已可直接根据“是什么”来下结论,由于这样的结论剔除了个人情绪、心理动机、抽样精确性等因素的干扰,因此,将更精确,更有预见性。不过,一些学者指出,由于“大数据”理论过于依靠数据的汇集,那么一旦数据本身有问题,在“只问有什么,不问为什么”的模式下,就很可能出现“灾难性大数据”,即因为数据本身的问题,而做出错误的预测和决策。

巴以冲突的历史由来:巴勒斯坦位于亚洲西部地中海沿岸,古称迦南,包括现在的以色列、加沙、约旦河西岸和约旦。历史上,犹太人和阿拉伯人都曾在此居住过。公元前20世纪前后,闪米特族的迦南人定居在巴勒斯坦的沿海和平原地区,成为巴勒斯坦最早的居民。公元前13世纪未,希伯莱各部落迁入巴勒斯坦,并曾先后建立希伯莱王国及以色列王国。此后巴勒斯坦又先后被亚述人、巴比伦人、波斯人及罗马人占领和统治。公元7世纪,阿拉伯人在战胜罗马帝国接管巴勒斯坦后不断迁入,并被当地土著人同化,逐渐形成了现代的巴勒斯坦阿拉伯人。19世纪末,犹太复国主义运动在世界各地兴起,各地的犹太人大批移入巴勒斯坦。第一次世界大战期间,巴勒斯坦沦为英国的“委任统治地”。英国将其分为两部分:即以约旦河为界把巴勒斯坦分为东西两部分,东部称外约旦(即今约旦王国),西部仍称巴勒斯坦(即今以色列、约旦河西岸和加沙地带)。此后,世界各地犹太人开始陆续移居巴勒斯坦地区。在犹太人纷纷涌入巴勒斯坦的过程中,犹太人与当地的巴勒斯坦阿拉伯人发生过多次流血冲突。1947年11月,联合国通过第181号巴勒斯坦分治决议。决议规定,在7万平方公里的巴勒斯坦领土上建立犹太国和阿拉伯国,耶路撒冷国际化。1948年5月14日,以色列国宣告成立。由于这项决议遭到巴勒斯坦人以及阿拉伯方面的强烈反对,巴勒斯坦国却未能诞生。以色列宣布建国后,阿以之间爆发了5次大规模战争。以色列通过战争占领了包括耶路撒冷在内的大量的巴勒斯坦领土,数百万巴勒斯坦阿拉伯人被逐出家园,沦为难民。长期以来,以色列在被占领的阿拉伯领土上实施犹太移民政策,大量兴建犹太移民定居点,力求通过改变其占领领土上的人口结构,建立一个大以色列国。为了恢复民族权利,重返家园,巴勒斯坦人开始了武装斗争。1964年5月,巴勒斯坦解放组织(简称“巴解组织”)成立,其目标就是要在“巴勒斯坦领土上消灭犹太复国主义”。从此,巴勒斯坦开始了反对以色列入侵的武装斗争。多年的战争使双方认识到,谁也无法消灭谁,战争解决不了问题。在国际社会的斡旋下,巴以双方开始寻找政治解决的途径。1991年10月马德里中东和会召开,阿以间开始艰难的和平谈判。在阿以和谈中,巴以和谈是构成中东和平进程的关键。1993年9月,巴以双方签署了第一个和平协议-巴勒斯坦自治《原则宣言》以来,双方还签署了一系列协议,然而这些协议由于以历届政府的有意拖延而未能彻底执行。尽管根据有关协议,1994年5月巴勒斯坦开始自治,但关于巴勒斯坦最后阶段谈判却因双方在耶路撒冷的归属、犹太人定居点、巴勒斯坦难民回归、巴以边界划定等棘手问题上分歧太大,巴以双方至今没有达成永久性和平协议。2000年9月,以强硬派领导人沙龙强行进入伊斯兰圣地阿克萨清真寺,引发了一场旷日持久的巴以流血冲突,特别是2001年3月沙龙政府上台以后,由于沙龙采取了一系列强硬政策,巴勒斯坦一些激进组织针对以色列人制造了一系列“恐怖活动”,致使以色列采取了强烈打击报复,巴以双方陷入报复与反报复的恶性循环。中东和平进程为了恢复民族权利,重返家园,巴勒斯坦人开始了武装斗争。1964年5月,巴勒斯坦解放组织(简称“巴解组织”)宣告成立,开始反对以色列入侵的武装斗争。此后,巴解组织改变谋求建国的斗争方式,开始以和平谈判来实现建国的漫长历程。1988年11月15日,巴解组织全国委员会第19次特别会议通过《独立宣言》,宣布建立以耶路撒冷为首都的巴勒斯坦国。此后有130多个国家先后承认巴勒斯坦国。由于没有自己的领土,巴勒斯坦国不是一个真正意义上的国家。1991年10月马德里中东和会召开,阿以间开始艰难的和平谈判。这是阿拉伯国家与以色列第一次坐到一起试图解决长达40多年的冲突。这次会议构筑了中东和谈的基本框架——和谈分成双边会谈和多边会谈两个层次,确立了以“土地换和平”的基本原则。1993年9月13日,巴以双方第一个和平协议——巴勒斯坦自治《原则宣言》在华盛顿签署。根据协议,巴勒斯坦人首先在加沙-杰里科地区实行自治,临时过度期为5年。根据1994年5月,巴以双方签署的关于实施加沙-杰里科自治原则宣言的最后协议,5月4日巴勒斯坦开始自治。1995年9月巴以双方签署了塔巴协议,以色列军队先后撤出约旦河西岸的7座主要城市,由巴方自治。1996年5月4日,巴以开始就关于巴勒斯坦最后阶段谈判进行了首轮会谈。但以色列在1996年6月内塔尼亚胡执政后,背弃以“土地换和平”的原则,强调以“安全换和平”的原则取而代之,使中东和平进程停滞不前。尽管巴以先后签署了《希伯伦协议》和《怀伊协议》,但终因以政府的拖延而未能彻底执行。1999年5月,巴拉克当选以色列总理。为落实怀伊协议,巴以签署了《沙姆沙伊赫备忘录》,双方同意1999年9月13日开始最终地位谈判,并于2000年2月15日前就耶路撒冷地位等问题达成框架协议,9月13日前达成最终协议。由于以方蓄意拖延,协议条款没有得到很好的执行。2000年7月巴以美三方首脑会晤在美国马里兰州的戴维营举行。因涉及耶路撒冷地位、边界划分、犹太人定居点前途、巴难民回归以及水资源分配等棘手问题,会谈未能达成协议。同年9月28日,以色列强硬派领导人沙龙强行进入伊斯兰圣地阿克萨清真寺,引发了巴以间一场旷日持久的流血冲突。2001年3月沙龙政府上台以后,巴以关系更加恶化。阿拉伯与以色列矛盾概况阿拉伯国家和以色列之间矛盾的实质是领土问题,双方的领土争端是在过去几十年中陆续形成的。1947年联合国安理会通过的巴勒斯坦分治决议,把总面积为2·6万多平方公里的巴勒斯坦领土一分为二,14477平方公里划给犹太人建以色列国,11655平方公里划给阿拉伯人建立巴勒斯坦,并将耶路撒冷暂定为“国际城市”,即归属未定。在以色列建国的第二天,即1948年5月15日爆发的阿以战争中,以色列吞并了划归给巴勒斯坦的6200多平方公里的土地,并强行占领了西耶路撒冷。当时的约旦国王阿卜杜拉占领了划归巴勒斯坦的约旦河西岸领土,包括东耶路撒冷,共5268平方公里。1967年第三次中东战争中,以色列占领了约旦河西岸和加沙地带,同时还占领了6000多平方公里的埃及西奈半岛、1600平方公里的叙利亚戈兰高地、埃及管辖的加沙地带,又从约旦手中夺走了东耶路撒冷,并宣布整个耶路撒冷为以色列的首都。1982年黎巴嫩战争中,以色列又占领了黎巴嫩南部一条10-15公里宽的狭长地带。根据1978年埃以达成的戴维营协议,以色列把西奈半岛归还了埃及。1974年,以色列曾把戈兰高地的一部分退还给叙利亚,但继续占领戈兰高地其余的700平方公里的土地,并于1981年宣布将其并吞。近几年来,以色列在它所占领的阿拉伯领土上大量兴建犹太移民定居点。在约旦河西岸和加沙地带,以色列已建立200个定居点,犹太移民达10·4万。以色列的犹太移民政策是谋求通过改变其占领的阿拉伯领土上的人口结构,建立一个从约旦河直至地中海的大以色列国。多年来,阿拉伯国家要求以色列遵照联合国242号和338号决议,在被占领土上停止兴建犹太移民定居点,撤出1967年其占领的领土,以“土地换和平”。以色列却认为,西奈半岛归还埃及后,它已完成履行联合国决议的要求,现在只需要以“和平换和平”。巴勒斯坦人民要求在被占领土上建立自己独立的国家,以色列却只顾同西岸和加沙地带的代表讨论“有限自治”问题。叙利亚要求以色列归还戈兰高地,黎巴嫩要求以色列撤出黎巴嫩南部,而以色列却一再表示坚持“寸土不让”。以巴分治和以色列建国公元70年,古罗马大军占领耶路撒冷,摧毁犹太教圣殿。公元135年,犹太人被逐出巴勒斯坦,由此开始了持续1800多年的漂泊生涯。从被逐出故土那天起,犹太人就没有忘记过重返故园。19世纪末,欧洲出现了大规模反犹太主义浪潮,犹太复国主义的思潮和运动也由此相应兴起。1881年,俄籍犹太医生平斯克尔出版了《自我解放》一书,提出了建立犹太民族国家的想法。该书被认为是犹太复国主义的发端。1896年,匈牙利犹太律师赫茨尔又出版了《犹太国》一书,完整地提出了犹太复国主义的思想。针对当时欧洲到处可以听到的“犹太人滚出去”的口号,他这样写道:“我现在要以最简单的形式提出这个问题:我们现在要‘出去’吗?到哪里去呢?”“应该把地球的某一部分的主权授予我们,其面积足以满足一个民族的正常需要;其余的事情将由我们自己来做。”赫茨尔的著作在犹太人中引起了很大的反响,但这个民族家园究竟建在何处,犹太人内部也有过分歧。他们设想过在南非和阿根廷,还认真考虑过乌干达,并为之进行过投票。直到1897年8月29日在瑞士巴塞尔召开的第一次世界犹太复国主义者代表大会,才将其最终定在犹太人心目中的文化根——巴勒斯坦。这次大会提出,犹太人应建立“一个得到公众承认的、有法律保障的家园(或国家)”。与此同时,“世界犹太复国主义组织”成立并开始活动。他们组织犹太人向许多世纪以来阿拉伯人聚居的巴勒斯坦移民,并成立了“犹太国民基金”和“巴勒斯坦土地开发公司”等相应机构。这次大会召开的1897年,被认为是犹太人将自己的家园梦想开始付诸实践的一年,也被认为是巴以争端的开始之年。从《贝尔福宣言》到《巴勒斯坦白皮书》第一次世界大战期间,巴勒斯坦被英军占领,战后成为英国的“委任统治地”。1917年11月2日,英国外交大臣贝尔福写信给犹太复国主义者联盟副主席罗斯查尔德,声称“英王陛下政府赞成在巴勒斯坦建立一个犹太人的民族国家,并将尽最大努力促其实现”。此信后被称为《贝尔福宣言》。犹太人据此开始向巴勒斯坦大批移民。但是,此举遭到巴勒斯坦当地阿拉伯人的强烈反对,他们以暴动和罢工的方式向英国施加压力,要求限制犹太人移民。这场动乱一直持续了3年之久。与此同时,在纳粹迫害下生计无着的犹太人继续向巴勒斯坦大批移民,至1939年,移居巴勒斯坦的犹太人总数已增加到5万人。1936至1939年期间,英国曾建议在巴勒斯坦分别建立一个犹太人国家(面积远比后来联合国划定的小)和一个阿拉伯人国家,但被阿拉伯人拒绝。1939年5月,英国政府害怕进一步激起阿拉伯各国的反抗,遂主动向阿拉伯各国示好,提出了所谓的《巴勒斯坦白皮书》。白皮书提出:在今后5年中,每年只限移入5万名犹太人;限制犹太人购买阿拉伯人的土地,准备把巴勒斯坦逐步移交给一个阿拉伯人占多数的当地政府,犹太人可在该政府管辖下实行高度自治。阿拉伯人的动乱是平息了,但是,在对立情绪强烈的犹太人与阿拉伯人之间建立信任,显然不是一件容易的事。《巴勒斯坦白皮书》公布之时,恰是欧洲犹太人为逃避纳粹大屠杀,苦苦寻求安身立命的绿洲之日。在纳粹惨绝人寰的大屠杀中,全世界1/3的犹太人被杀害,遇难者总数达600万,欧洲犹太人所剩无几。英国在向德国宣战前,由于坚持白皮书的立场,不让受迫害的德国和奥地利犹太人进入巴勒斯坦,使得当地犹太人和托管当局处在了战争边缘。只是基于对德国法西斯的共同仇恨,才使暴力活动有所限制。但是,在战时,犹太突击队从未停止过对拦截非法移民的英军设施的破坏。联合国第181号决议和以色列立国二战结束后,从纳粹集中营里解放出来的几十万波兰犹太囚徒,成了无家可归之人。他们不能返回故园,因为此时在波兰各地相继发生了杀害返乡犹太人的事件;除了几个北欧国家之外,饱受战争蹂躏的西欧国家无力收容他们;连素以移民国家著称的美国都不愿敞开大门。此时,惟一张开臂膀欢迎他们的,就是巴勒斯坦的犹太社区。由于英国继续坚持白皮书的政策,导致犹太突击队同英国托管当局的冲突不断升级。犹太人炸路断桥,袭击拘禁非法移民的营地,暗杀英国官员。对英国而言,这将是一场不得人心的战争。此时,希特勒杀害600万犹太人的罪行,正被逐步揭露,国际舆论一边倒地同情犹太人。让那些被解放的波兰犹太人继续住集中营,实在是说不过去。随着轴心国秘密文件的曝光,英国当年拒绝意大利的提议、不同意德国和奥地利犹太人经意大利转送巴勒斯坦的决定,也大白于天下,舆论视英国为残杀犹太人的帮凶。在国际舆论的压力下,英国决定从巴勒斯坦脱身。1947年2月15日,英国宣布把巴勒斯坦这块烫手山芋转交联合国。1947年11月29日,第二届联合国大会以33票赞成、13票反对(其中10个是伊斯兰国家)、10票弃权的结果,表决通过了巴勒斯坦分治的决议,即联合国第181号决议。决议规定:英国于1948年8月1日之前结束在巴勒斯坦的委任统治,并撤出其军队;两个月后,在巴勒斯坦的土地上建立两个国家,即阿拉伯国和犹太国。根据分治决议的蓝图,阿拉伯国国土可达11203平方公里,约占当时巴勒斯坦总面积的43%,人口中阿拉伯人为5万人,犹太人为1万人;犹太国国土为14942平方公里,约占巴勒斯坦总面积的57%,人口中阿拉伯人为7万人,犹太人为8万人。决议还规定:成立耶路撒冷市国际特别政权,由联合国来管理。苏联出于争取以色列执政的工党的考虑,一改从帝俄时期就固有的反犹态度,为以色列建国出了大力,并对以色列国的建立和巩固给予了外交和军事上的支持。苏联常驻联合国代表葛罗米柯在联大一番感人的演讲,对181号决议的顺利通过起了重要作用。而曾在《贝尔福宣言》中信誓旦旦地表示支持犹太人复国的英国,却在此时投了弃权票。当时,巴勒斯坦地区的阿拉伯人有120多万,占总人口的2/3强。但分治决议中的阿拉伯国的领土只占巴勒斯坦总面积的43%。更令阿拉伯人难以容忍的是,阿拉伯国的领土支离破碎,互不相连,大部分是丘陵和贫瘠地区。犹太国则不然,犹太人虽仅有60万,不到总人口的1/3,然而其领土却占巴勒斯坦总面积的57%,大部分又位处沿海地带,土地肥沃。1948年5月14日下午,特拉维夫现代艺术博物馆前面的广场上,挤满了犹太人。下午4时,身高6米的“以色列建国之父”本—古里安宣布《以色列国独立宣言》。本—古里安就任以色列第一任总理。以色列建国的消息通过电波传遍了全世界,大部分国家作出了积极的反应。本—古里安宣布建国17分钟后,美国白宫新闻秘书查理·罗斯向记者宣布:美国承认以色列。承认以色列的文告是美国人在还不知道这个新国家叫什么名字的时候就拟好的。当得知这个国家取名“以色列”时,杜鲁门总统用笔将文告上的“犹太国”字样划去,改为“以色列”。5月17日,苏联宣布承认以色列。建国次日即爆发战争1948年5月15日,也就是以色列宣布建国的第二天,英国宣布结束在巴勒斯坦的委任统治。当天,阿拉伯联盟国家埃及、伊拉克、黎巴嫩、叙利亚以及外约旦(1950年改称约旦)的军队相继进入巴勒斯坦,同时,阿拉伯联盟发表声明,宣布对以色列处于战争状态,第一次中东战争由此爆发。这次战争史称“巴勒斯坦战争”。与以后的几次中东战争不同,英美两国出于在阿拉伯世界的长远战略考虑,在巴勒斯坦战争中站到了阿拉伯人一边。倒是苏联为争取这个新生的国家,对以色列给予了充分的支持。当时在苏联控制之下的捷克斯洛伐克不仅为以色列提供了大量的军火,而且为以色列提供专用机场、建立空中走廊,为以色列训练空军和伞兵部队。战争进行之时,几名驻欧美国空军犹太裔士兵冒着军法审判的危险,偷了3架重型轰炸机,在捷克斯洛伐克的机场装满炸弹后,起飞轰炸开罗和大马士革。由于参战的阿拉伯各国彼此之间心存疑忌、内部不和,外约旦国王阿卜杜拉和埃及国王法鲁克各打算盘,使得只有游击队实力的以色列取得了战争的主动权。7月中旬,在英、美的催促下,以色列宣布停火,但零星战斗持续到1949年。这次战争后,巴勒斯坦被分为三部分:以色列占领了巴勒斯坦总面积的78%,超过“分治决议”规定面积5700多平方公里;约旦河西岸归约旦管辖;加沙地带归埃及管辖。近百万巴勒斯坦人被逐出家园成为难民。第一次中东战争的失败使周围阿拉伯国家备感耻辱,到处弥漫着革命的气息。1949年3月、8月和12月,叙利亚先后3次发生政变。1951年7月,约旦国王阿卜杜拉父子被巴勒斯坦难民刺杀。阿卜杜拉国王18岁的孙子侯赛因由于子弹击中了祖父亲手别在他胸口上的一枚勋章而幸免于难,于1953年继位成为约旦哈希姆王国国王。1952年7月,埃及军人推翻法鲁克王朝,自由军官组织领导人纳赛尔于1956年6月成为总统。五次中东战争简介第一次中东战争(1948—1949):又称巴勒斯坦战争,以色列称“独立战争”。1948年5月14日,以色列宣布建国。次日凌晨,外约旦、伊拉克、叙利亚、埃及等阿拉伯国家出兵进攻以色列。第二次中东战争(1956—1957):又称苏伊士运河战争,以色列称“西奈战役”。1956年10月,英、法、以色列借口埃及宣布苏伊士运河公司收归国有和禁止以船只通过运河与蒂朗海峡,联合向埃及发动进攻。第三次中东战争(1967):又称“六五战争”,阿拉伯国家称“六月战争”,以色列称“六天战争”。1967年,以色列借口埃及封锁亚喀巴湾,于6月5日晨,对埃及、叙利亚、约旦发动突然袭击。第五次中东战争(1982年6月—9月):又称黎巴嫩战争。1982年6月6日,以色列出兵占领黎巴嫩14的领土,袭击黎巴嫩境内的巴解组织及其武装力量,并与在黎的叙利亚军队交战。从历史的角度分析

回答 您好,您的问题已看到,正在为您解答,请稍等。我是百度特邀答主,擅长解答有关教育领域的各种问题很高兴为您服务 现在是资讯科技的时代,但是网络中还是隐藏着无限的危机,因此“网络安全”已经变成每个人都应该重视的事情了。像为了确保个人资料不外漏,我们应该做好安全措施,才不会使个人资料、照片…等重要资料让别人知道,虽然网际网络带给我们很大的便利,但是也有许多人使用木马、病毒…等各式各样的诈骗以及威胁资讯安全的方法盗取别人的重要资料,所以为了保障个人的重要资产,我门应做以下措施,以确保资料安全:1、电脑不用时要注销2、个人资料应备份3、浏览网络要小心4、电子邮件要过滤5、不明网站不乱开6、软体使用要版权,如果做好以上措施,就可以让重要资料多一份保障哦!还有许多人会使用网络进行资料查询、交作业、工作或聊天…等事情,但是这些人不见得是使用正确得方法去使用电脑,也有一些人很会用电脑玩游戏和写报告,可是,如果没有适当的使用电脑,就很有可能造成反效果哦!还有还有,现在不论文字、影音、图片…等都可以在网络上快速传送,是知识财产权更容易受到侵犯,知识财产权的范围非常广,包括:图片、音乐、影音软体…等等,因此在引用时,应取的作者的授权哦!为了安全起见,上网一定要小心,浏览页面时也要谨慎,如过做到以上叙述的事项,就可以保障自己的权利,也不会触犯到法律 网络已经融入到我们生活之中,是我们信息交流不可缺少的工具,给现代的文化科技做出了很重要的贡献。我们这一代人必须要懂电脑,会电脑。但是它也不是那么“忠诚”,会给我们带来很大的危害,我们只有用的好,用得妙,才能达到理想的效果。首先,危害最大的就是游戏,在虚拟的游戏中,会因为游戏的好玩和自如而沉迷,无法自拔。从而对网络产生依赖。而且在网上任何人都模糊不清,任何错误无需承担,便随心所欲为所欲为。如果带到现实生活中那后果会不堪设想。而且上网时会遇到各种对我们不好的信息,会让我们在无意中受到伤害。长时间的玩电脑会对我们的身体造成不良影响。而且整天沉溺于网络,对学习产生了很大的影响,从而荒废了学生业。我们怎样才能从网络中找回自己呢?最重要的是家长,因为家长在孩子的身边的时候最多,家长应该多多正确的引导和监督,遇到问题与孩子多谈心好好沟通,其次,学校也应该多开展一些健康上网的活动,不仅娱乐而且还可以增长知识。我们也可以多参加一些有趣的活动,多读一些书。上网有利有弊,好好运用利大于弊,假如迷恋网络,便弊大于利,利弊就在一念之间,我们要好好的利用网络,让他成为我们的好助手,好朋友。而不是沉迷的工具。 这个是两个范文您可以看一下 希望对您有所帮助 更多2条 

大数据与网络安全论文范文初中

回答 您好,您的问题已看到,正在为您解答,请稍等。我是百度特邀答主,擅长解答有关教育领域的各种问题很高兴为您服务 现在是资讯科技的时代,但是网络中还是隐藏着无限的危机,因此“网络安全”已经变成每个人都应该重视的事情了。像为了确保个人资料不外漏,我们应该做好安全措施,才不会使个人资料、照片…等重要资料让别人知道,虽然网际网络带给我们很大的便利,但是也有许多人使用木马、病毒…等各式各样的诈骗以及威胁资讯安全的方法盗取别人的重要资料,所以为了保障个人的重要资产,我门应做以下措施,以确保资料安全:1、电脑不用时要注销2、个人资料应备份3、浏览网络要小心4、电子邮件要过滤5、不明网站不乱开6、软体使用要版权,如果做好以上措施,就可以让重要资料多一份保障哦!还有许多人会使用网络进行资料查询、交作业、工作或聊天…等事情,但是这些人不见得是使用正确得方法去使用电脑,也有一些人很会用电脑玩游戏和写报告,可是,如果没有适当的使用电脑,就很有可能造成反效果哦!还有还有,现在不论文字、影音、图片…等都可以在网络上快速传送,是知识财产权更容易受到侵犯,知识财产权的范围非常广,包括:图片、音乐、影音软体…等等,因此在引用时,应取的作者的授权哦!为了安全起见,上网一定要小心,浏览页面时也要谨慎,如过做到以上叙述的事项,就可以保障自己的权利,也不会触犯到法律 网络已经融入到我们生活之中,是我们信息交流不可缺少的工具,给现代的文化科技做出了很重要的贡献。我们这一代人必须要懂电脑,会电脑。但是它也不是那么“忠诚”,会给我们带来很大的危害,我们只有用的好,用得妙,才能达到理想的效果。首先,危害最大的就是游戏,在虚拟的游戏中,会因为游戏的好玩和自如而沉迷,无法自拔。从而对网络产生依赖。而且在网上任何人都模糊不清,任何错误无需承担,便随心所欲为所欲为。如果带到现实生活中那后果会不堪设想。而且上网时会遇到各种对我们不好的信息,会让我们在无意中受到伤害。长时间的玩电脑会对我们的身体造成不良影响。而且整天沉溺于网络,对学习产生了很大的影响,从而荒废了学生业。我们怎样才能从网络中找回自己呢?最重要的是家长,因为家长在孩子的身边的时候最多,家长应该多多正确的引导和监督,遇到问题与孩子多谈心好好沟通,其次,学校也应该多开展一些健康上网的活动,不仅娱乐而且还可以增长知识。我们也可以多参加一些有趣的活动,多读一些书。上网有利有弊,好好运用利大于弊,假如迷恋网络,便弊大于利,利弊就在一念之间,我们要好好的利用网络,让他成为我们的好助手,好朋友。而不是沉迷的工具。 这个是两个范文您可以看一下 希望对您有所帮助 更多2条 

论文正文:(1)引言:引言又称前言、序言和导言,用在论文的开头。引言一般要概括地写出作者意图,说明选题的目的和意义,并指出论文写作的范围。引言要短小精悍、紧扣主题。〈2)论文正文:正文是论文的主体,正文应包括论点、论据、论证过程和结论。主体部分包括以下内容:提出-论点;分析问题-论据和论证;解决问题-论证与步骤;结论。发你一份参考

安全伴我行安全,牵系着每一个人的生活。每当我走在上学、放学的路上,看到“车水马龙”,“人山人海”的热闹景象,看到身边飞驰而过的车辆,心里就会产生恐惧感。眼前浮现的一幕幕车毁人亡的画面,让我感到害怕。每当想到这里,我就十分紧张,真害怕第二天遇到车祸的就是我。大家可能看到过这样一个报道:2005年11月14日,是个阳光明媚的日子。山西沁源县第二中学的几百名师生正在马路边跑操,突然间,一辆大货车象一个发疯的恶魔碾向跑操的队伍,随着一片片惊呼和惨叫,21个鲜花般的生命永远的离开了这美好的世界。许多家长听到噩耗传来,一路上呼唤着孩子的名字,奔向现场,可是,任凭大人们怎样撕心裂肺地呼喊,他们永远也不能回应。这血的教训,给多少家庭带来痛苦,把多少幸福的家庭拆散。我国是一个人口大国,人多车多,使道路显得更加拥挤。据统计,我国每年因车祸死亡人数超过10万人,其中,儿童死亡人数近2万人,居世界之首。平均每5分钟就有1人死于车祸,而不到半小时就有一个孩子葬身车轮,这是多么惊人的数字。在这触目惊心的数字背后,有多少个家庭失去欢乐,多少个亲人痛不欲生,多少个生命之花永远凋零。想到这些,我抑制不住内心的激动,为遇难者留下同情的泪水,对肇事者产生无比的愤慨!然而,这些事故的发生,绝大多数都是因为人们的交通安全意识淡薄,不遵守交通法规造成的。作为一名合格的中学生,我们理应积极行动起来,从我做起,从身边做起。因此,我倡议:①全体同学要认真遵守《中学生守则》、《中学生日常行为规范》和交通法规。②校内文明守纪,楼道内轻声轻步,绝不打闹,不做危险的游戏。③校外一定要注意交通安全,走路要走人行道,过马路要走斑马线,不要翻越护栏。十字路口一定要看清红绿灯。④马路上行走时要集中精力,不看书、不听音乐、不打闹。“红灯短暂,生命无限”、“不怕百步远,只怕一步险”。其实,前人发明红绿灯是有原因的,不要怕麻烦,有句话说的好“红灯无数次,生命只一次”,红灯会闪烁无数次的,而生命只有一次,用完了就没有下一次了,在红灯没有灭的时候,我们绝对不可以冒险过马路,哪怕两边没有车,也绝对不能穿过马路。因此,同学们千万不要在马路上打闹,这样太危险。还有的惨剧是行人翻越护栏造成的,大家要不怕麻烦绕过护栏。为了我们的生命之花永远绽放,为了让所有的家庭幸福美满,亲爱的同学们,让安全永远伴随你我他吧!

你去知网、万方、维普找找参考论文,

网络安全与国家安全论文范文英文版

可以直接google里面打中文 自动 翻译 如果你连这3000千字都不想打 你连这4年父母辛苦给你的学费都是糟蹋

Data Management1 why Data Management ? We have already considered hardware and software in some In this chapter, we turn our attention to a third basic computer resource, Many computer applications require that data be stored for subsequent [1] Simply storing the data is not enough, A typical computer system, even a small one, can have dozens of disks and tapes, each holding data for dozens of different For any given application, one and only one set of data will We must be able to store, Locate, and retrieve the specific data needed by a given That is the concern of data 2 Accessing DataImagine a single diskette containing several For a particular application, only one of those programs will How is a given program selected, loaded, and executed? In Chapter 6, we learned that the operating system, responding to a use’s command, reds the disk’s index, searches it for the requested program name, extracts the program’s track and sector address, and issues primitive commands to read it into main Later, following a RUN command, the program is given control of the Accessing data presents a similar A single diskette can hold data for several different For a given application, one and only one set of data will do, and finding the right data is much like finding the right There are differences between accessing programs and accessing data, When a program is need, all its instructions must be loaded into Data, on the other hand, are typically processed selectively, a few elements at Thus, it is not enough merely to locate the data; we must be able to distinguish the individual data elements, 1 Data Structures The key to retrieving data is remembering where they are stored, If the data elements are stored according to a consistent and well understood structure, it is possible to retrieve by remembering that The simplest data structure is a For example, data for a program that computes an average might be stored as a series of numbers separated by commas (F1) The commas distinguish the individual data Most programming languages support amore complex data structure called an array (Fig 2) Each array element can hold one data Each element is assigned a unique identifying number or numbers, and individual data elements can be inserted, extracted, or manipulated by referencing those For example, in the array pictured in F 2 elements are identified by a row number and a column number, and row 1, column3 (element1,3) contains the value Once an array has been filled, it can be written to disk, tape, or any other secondary medium, and back into memory for Consider a program that generates name and address For each label, we need a name, a street address, a city, a state, and a zip If we needed only a few labels, we might store the data in a list, but separating the elements would soon become An option is to set up an array of names and addresses, with each row holding the data for a single The only problem is that the entire array must be in main memory before the individual elements can be accessed, and main memory space is Thus, even with an array, we could generate relatively few F 1 The simplest data structure is a Separators, such as these commas, serve to distinguish individual Often, a “sentinel” value, such as a negative number, marks the end of the 4410, 843, 184, 31, 905, 6357, 44, 7702, 228, 59, -1 F 2 Most programming languages support a more complex data structure called an array Individual cells are assigned a number or numbers, and data values are inserted manipulated, and extracted by referencing those A better solution is to organize the data as a file (F3) All computer data begin as patterns of bits, On a file, the bits are grouped to form Groups of characters, in turn, form meaningful data elements called A group of related fields is a record the file is a set of related For example, in a name and address file, an individual’s name is a Each record holds a complete set of data for data for a single individual ( a name, a street address, and so on) he file consists of all the Fig 3 Characters are grouped to form Fields are prouped to form A file is a group of related The data in a file are processed record by Normally, the file is stored on a secondary medium such as Programs are written to read a process its fields, generate the appropriate output, and then read and process another Because only one record is in main memory at a time, very little memory is Because many records can be stored on a single disk, a great deal of data can be processed in this limited 2 Locating Files Imagine a file stored on The first step in accessing its data is finding the The task is much like finding a program, but there are Following a command such as LOAD or RUN, programs are loaded by the application Data, on the other hand, are processed by application programs, in the context of a program’s Typically, just before the data are required, the program asks the operating system to open the Each file has a name; the open logic ( 4 ) reads the index, searches it by name, and finds the address of the first record in the F4 when a file is opened, the disk index is read into main memory and searched for the desired file’s If the file name is found, the file’s start address is extracted from the 3 Locating Records Once a file has located, the process of accessing its records can When a program needs input data, it reads a record; when it is ready to output results, it writes a Note that these instructions deal with selected records, not with the entire We open We read and write Let’s examine the data accessing process more A programmer views data logically, requesting the next record, or the name and address for a particular The data are stored on a secondary medium such as To access a record physically, the disk drive must be give a set of primitive commands: seeks, reads, and The programmer thinks in terms of logical I/O The external device stores and retrieves physical sectors; it “thinks” in terms of physical I/O There must be a mechanism for translating the programmer’s logical requests to the appropriate physical commands (Fig 5) On small computers, much of the logic is found in the operating system’s input/output control system; on larger machines, access methods are Increasingly, the programmer’s logical data request is translated to physical form by a database management 4 The Relative Record Concept How does software, be it operating system, access method, or database software, find specific records in a file? [2] The key to many storage and retrieval techniques is the relative record Imagine a string of 100 Numbers indicate a given record’s position relative to the first record in the The file’s first record ( relative record 0 ) is at “ start of file plus 0 ”;Its second record is at “ start of file plus 1”, and so Access Methods Imagine preparing meeting announcements for a You need a set of mailing labels, and each member’s name and address is recorded on an index Probably the easiest way to generate the labels is to copy the data from the first card, turn to the second card and copy it, and so on, processing the records sequentially, form the beginning of the file to the Magazine publishers face the same problem with each new issue, but need mailing labels for tens of thousands of Rather than using index cards, they store customer data on disk or magnetic tape, one record per The easiest way to ensure that all labels are generated is to process the records in the order in which they are stored, proceeding sequentially from the fist record in the file to the To simplify handing, the records might be presorted by zip code or a mailing zone, but the basic idea of processing the data in physical order still How dos this relate to the relative record number concept? A relative record number indicates a record’s position on the With sequential access, processing begins with relative record 0, then moves to relative record 1, 2, and son Accessing data sequentially involves little more than For example, imagine a program has just finished processing relative record What is the next record? Obviously, relative record We’ve already seen how a relative record number can be converted to read them, or write them, in physical Processing records in sequence is not always For example, when a subscriber moves, his or her address must be changed in the fire searching for that subscriber’s record sequentially is like looking for a telephone number by starting with the first page of the telephone book and reading line and That’s no how we use a telephone Instead, knowing the record are stored in alphabetical order ,we quickly narrow our search to a portion of a single page and then begin reading the entries, ignoring the bulk of the data the way we use a telephone book is good example of direct, or random, A disk drive reads or writes one record at a To randomly access a specific record, all the programmer must do is remember its address, and ask for it the problem is remembering all those disk addresses, One solution is maintaining an index of the Again, we’ll use the name and address fire as an We want to access individual customer record by As the file is created, records are written one at a time, in relative record number Additionally, as each record is written, the customer name and the associated relative record number are recorded in an array or After the last record has been written to disk and its position recorded on the index, the index is itself Once the index has been created, it can be used to find individual Assume, for example, that Susan Smith has changed her To record her now address on the file, a program read the file index, search the index for her name, find her relative record number, compute the disk address, and read her record, change her address, rewrite the record to the same place on Note that this specific record is accessed directly, and that no other records in the file are The basic idea of direct access is assigning each record an easy to remember, logical, and then converting that key to a relative record number, Given this relative location, a physical address can be computed, and record Using an index is one technique for converting keys to physical An option is passing a numeric key to an algorithm and computing a relative record Both techniques have the same objective; converting a programmer’s logical data requests to physical Earlier in the chapter we identified the gap separating logical and physical I/O An access method is a software module that bridges this gap, converting logical keys to physical addresses, and issuing the appropriate primitive There are many variations of sequential, indexed, and direct organizations, and each one has its own access Using a variety of data access techniques can be confusing, and this is one reason for the growing popularity of database management systems4 Database Management There are problems with traditional data Many result from viewing applications For example, consider Most organizations prepare their payrolls by computer because using a machine instead of a small army of clerks saves Thus, the firm develops a payroll program to process a payroll file, Inventory, accounts receivable, accounts payable, and general ledger analysis are similar applications, so the firm develops an inventory program, and inventory file, an accounts receivable program, an accounts receivable file, and so Each program is independent, and each processes it own independent data Why is this a problem? For on thing, different application often need the same data For example, schools generate both bills and student grade View the applications The billing program reads a file of billing data, and the grade report program reads an independent file of grade The outputs of both program are mailed to each student’s home; thus, student names and addresses must be redundantly recorded on both What happens when a student moves? Unless both file are up data, one will be Redundant data are difficult to A more subtle problem is data Each access method has its own rules for storing and retrieving data, and certain “tricks of the trade” can significantly improve the efficiency of a given Bacause the motivation for using the computer is saving The programmer is often tempted to save even more by taking advantage of these Thus, the program’s logic becomes dependent upon the physical structure of the When a program’s logic is tied to its physical data structure, changing that structure will almost certainly require changing the As a result, programs using traditional access method can difficult to The solution to both problems is often organizing the data as a single, integrated The task of controlling access to all the data can then be concentrated in a centralized database management How dose the use of a centralized database solve the data redundancy problem? All data are collected and stored in a single place; consequently, there is one and only one of any given data When the value of an element ( an address, for example) changes, the single database copy is corrected, Any program requiring access to this data element gets the same value, because there is only on How dose a database help to solve the data dependency problem? Since the responsibility for accessing the physical data rests with the database management system, the programmer can ignore the physical data As a result, programs tend to be much less dependent upon their data, and generally much easier to Expect the trend toward database management to There are problems with traditional data Because different applications often require the same data, certain data elements may be stored in several different places, and such redundant data are difficult to Another problem is data If a program’s logic is too closely linked to the physical structure of its data, that program can be difficult to The solution to both problems is often collecting all the organization’s data in a centralized With a database, there is only one copy of each data element, so the data redundancy problem is Because every program must access data through a database management system, programs are insulated from the physical data structure; thus, data dependency is

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看见这种问题就烦现在大学生都怎么了。我是中专毕业的。我的毕业设计我自己做了半年。我感觉真的受益匪浅。劝你也放弃拿来主义吧。多掌握点东西绝对没有坏处。

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